Robotic finger assembly

ABSTRACT

A robotic hand includes a finger with first, second, and third phalanges. A first joint rotatably connects the first phalange to a base structure. A second joint rotatably connects the first phalange to the second phalange. A third joint rotatably connects the third phalange to the second phalange. The second joint and the third joint are kinematically linked such that the position of the third phalange with respect to the second phalange is determined by the position of the second phalange with respect to the first phalange.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 12/564,078, filed Sep. 22, 2009, and which is hereby incorporated byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under NASA Space ActAgreement number SAA-AT-07-003. The government may have certain rightsin the invention.

TECHNICAL FIELD

The present invention relates to robotic hands, and more particularly torobotic fingers.

BACKGROUND OF THE INVENTION

Typical robots are automated devices that are able to manipulate objectsusing a series of rigid links, which in turn are interconnected viaarticulations or motor-driven robotic joints. Each joint in a typicalrobot represents an independent control variable, also referred to as adegree of freedom (DOF). End-effectors are the particular links used forperforming a task at hand, e.g., grasping a work tool or an object.Therefore, precise motion control of a robot may be organized by thelevel of task specification: object level control, i.e., the ability tocontrol the behavior of an object held in a single or cooperative graspof a robot, end-effector control, and joint level control. Collectively,the various control levels cooperate to achieve the required roboticmobility, dexterity, and work task-related functionality.

Humanoid robots in particular are robots having an approximately humanstructure or appearance, whether a full body, a torso, and/or anappendage, with the structural complexity of the humanoid robot beinglargely dependent upon the nature of the work task being performed. Theuse of humanoid robots may be preferred where direct interaction isrequired with devices or systems that are specifically made for humanuse. Due to the wide spectrum of work tasks that may be expected of ahumanoid robot, different control modes may be simultaneously required.For example, precise control must be applied within the different spacesnoted above, as well as control over the applied torque or force,motion, and the various grasp types.

SUMMARY OF THE INVENTION

A robotic hand assembly includes a base structure; a finger havingfirst, second, and third phalanges; a first joint operatively connectingthe first phalange to the base structure such that the first phalange isselectively rotatable with respect to the base structure about a firstaxis; a second joint operatively connecting the second phalange to thefirst phalange such that the second phalange is selectively rotatablewith respect to the first phalange about a second axis; and a thirdjoint operatively connecting the third phalange to the second phalangesuch that the third phalange is selectively rotatable with respect tothe second phalange about a third axis.

The third joint is kinematically linked to the second joint such thatthe position of the third phalange with respect to the second phalangeis determined by the position of the second phalange with respect to thefirst phalange. The kinematic linkage between the second and thirdjoints replaces one of the degrees of freedom of a human finger whileclosely approximating the movement of a human finger.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective illustration of a dexterous humanoidrobot having two hands;

FIG. 2 is a schematic perspective illustration of an upper arm for thedexterous humanoid robot of FIG. 1;

FIG. 3 is a schematic perspective illustration of a lower arm for thedexterous humanoid robot of FIGS. 1 and 2;

FIG. 4 is a schematic, perspective view of a finger of one of the handsof FIG. 1 in a first position;

FIG. 5 is a schematic, perspective view of the finger of FIG. 4 in asecond position; and

FIG. 6 is a schematic, perspective view of the finger of FIGS. 4 and 5in a third position;

FIG. 7 is a schematic, side view of a portion of the finger of FIG. 4;

FIG. 8 is another schematic, side view of the portion of the finger ofFIG. 7;

FIG. 9 is a schematic, side view of the finger of FIG. 4 depictingtendon routing;

FIG. 10 is a graph depicting the position of one of the joints in thefinger as a function of the position of another one of the joints in thefinger;

FIG. 11 is a schematic, top view of the thumb of FIG. 4 depicting tendonrouting;

FIG. 12 is a schematic, perspective view of the finger of FIG. 4 mountedto base structure by a shock mount;

FIG. 13 is a schematic, side view of a sensor assembly at a joint of thefinger of FIG. 4;

FIG. 14 is a schematic, perspective view of the shock mount of FIG. 12;

FIG. 15 is another schematic, perspective view of the finger of FIG. 4;

FIG. 16 is yet another schematic, perspective view of the finger of FIG.4;

FIG. 17 is yet another schematic, perspective view of the finger of FIG.4;

FIG. 18 is a schematic, perspective, cutaway view of a phalange andsensor assembly that is representative of the phalanges of the finger ofFIG. 4; and

FIG. 19 is a schematic, exploded view of the phalange and sensorassembly of FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings, wherein like reference numbers refer tothe same or similar components throughout the several views, FIG. 1shows a dexterous humanoid robot 10 adapted to perform one or more taskswith multiple degrees of freedom (DOF).

The humanoid robot 10 may include a head 12, torso 14, waist 15, arms16, hands 18, fingers 19A-19D, and thumbs 21, with various joints beingdisposed within or therebetween. The robot 10 may also include atask-suitable fixture or base (not shown) such as legs, treads, oranother moveable or fixed base depending on the particular applicationor intended use of the robot. A power supply 13 may be integrallymounted to the robot 10, e.g., a rechargeable battery pack carried orworn on the back of the torso 14 or another suitable energy supply.

According to one embodiment, the robot 10 is configured with a pluralityof independently and interdependently-moveable robotic joints, such asbut not limited to a shoulder joint assembly (arrow A), an elbow jointassembly (arrow B), a wrist joint assembly (arrow C), a neck jointassembly (arrow D), and a waist joint assembly (arrow E), as well as thevarious finger and thumb joint assemblies (arrow F) positioned betweenthe phalanges of each robotic finger 19A-19D and thumb 21.

The arm 16 is divided into an upper arm 22 and a lower arm (or forearm)24. The upper arm 22 extends from the shoulder joint assembly (arrow A)to the elbow joint assembly (arrow B). Extending from the elbow joint(arrow B) is the lower arm 24, hands 18, fingers 19, and thumbs 21. Forthe purpose of simplification, as described herein, the upward directionis toward the head 12 and the downward direction is toward the waist 15.Those skilled in the art will appreciate that since the robot 10 isintended to simulate a humanoid, the robot will be substantiallysymmetrical about a vertical plane bisecting the torso and head, andessentially include an identical symmetrical structure on both the leftand right sides.

Referring to FIG. 2, the upper arm 22 is illustrated. Although only oneupper arm 22 for the arms 16 is shown, both the left and the right arms16 operate in the same manner as described below. The upper arm 22 has ashoulder joint assembly (arrow A) that includes a first shoulder jointS1 providing a first DOF, and second shoulder joint S2 providing asecond DOF, and a third shoulder joint S3 providing a third degree offreedom. Together the first through third shoulder joints S1, S2, S3perform the movements that represent the movements a human shoulder canperform. Specifically, rotation of the first shoulder joint S1 about afirst shoulder axis SA1 moves a second shoulder axis SA2 for the secondshoulder joint S2 into a desired position. Based upon the position ofthe first shoulder joint S1, rotation of the second shoulder joint S2about the second shoulder axis SA2 then moves the arm 16 up and downrelative to the torso 14, or forward and backward relative to the torso14. The third shoulder joint S3 rotates the upper arm 22 about a thirdshoulder axis SA3. Rotation of the third shoulder joint S3 rotates theupper arm 22 axially, i.e. rotation of the third shoulder joint S3rotates the elbow joint assembly (arrow B) to face upwards or downwards.Therefore, together the first shoulder joint S1, the second shoulderjoint S2, and the third shoulder joint S3 form the motions of a shoulderjoint assembly (arrow A).

The upper arm 22 also includes an elbow joint assembly (arrow B) whichincludes a first elbow joint L1 and a second elbow joint L2. The firstelbow joint L1 and second elbow joint L2 each provide a degree offreedom. Together the first elbow joint L1, and the second elbow jointL2 perform the movements that represent the movements a human elbow canperform. Rotation of the first elbow joint L1 about a first elbow axisB1 causes the upper arm 22, below the elbow joint assembly (arrow B) tobend and straighten. Additionally, rotation of the second elbow joint L2about a second elbow axis B2 causes the upper arm 22, below the elbowjoint assembly (arrow B) to rotate axially, i.e. rotation of the secondelbow joint L2 about the second elbow axis B2 rotates the lower arm 24and hand 18 (FIG. 1) to face palm up or down.

FIG. 3 illustrates the lower arm 24, including the wrist joint assembly(arrow C), the hand 18, the fingers 19A-19D, and thumb 21. The lower arm24 includes a plurality of finger (and thumb) actuators 26 and aplurality of wrist actuators 28. Additionally, a plurality of controls30 for the finger actuators 26 and the wrist actuators 28 are alsosupported on the lower arm 24. The lower arm 24 is attached to a loadcell 32 which is used to connect the lower arm 24 with the upper arm 22.The hand 18 includes a base structure 34 that defines the palm 36 of thehand 18. Fingers 19A-19D and thumb 21 are movably mounted to the basestructure 34 and selectively curl toward the palm 36 in order to grip anobject, such as the one shown at 20 in FIG. 1.

In the embodiment depicted, the hand 18 is comparable in size to that ofa sixtieth to eight-fifth percentile human male hand. More specifically,in the embodiment depicted, the length of the hand 18 is 7.9 inches(eightieth percentile human); the breadth, or width, of the hand 18 is3.6 inches (sixtieth percentile human); and the circumference of thehand (around the base structure) is 8.8 inches (eighty-fifth percentilehuman).

Referring to FIGS. 4-7, finger 19A corresponds in position and functionto a human index finger. Finger 19A includes a base member 37operatively connected to the base structure 34 of the hand 18. Thefinger 19A also includes a plurality of rigid links, or phalanges38A-38D, and four joints 42A-42D. Joint 42A operatively connectsproximal phalange 38A to the base structure 34 such that the phalange38A is selectively rotatable with respect to the structure 34 about axisA1. Joint 42B rotatably mounts phalange 38B to phalange 38A such thatphalange 38B is selectively rotatable with respect to phalange 38A aboutaxis A2. Joint 42C rotatably mounts phalange 38C to phalange 38B suchthat phalange 38C is selectively rotatable with respect to phalange 38Babout axis A3. Axes A1, A2, and A3 are parallel to one another.

In the embodiment depicted, the proximal phalange 38A is operativelyconnected to the base structure 34 by phalange 38D, joint 42D, and basemember 37. More specifically, joint 42A rotatably mounts phalange 38A tophalange 38D; joint 42D rotatably mounts phalange 38D to the base member37 such that phalange 38D, and, correspondingly, phalanges 38A-38C, areselectively rotatable with respect to the base member 37 and the basestructure 34 about axis A4. Axis A4 is perpendicular to axes A1, A2, andA3. Thus, joint 42D permits rotation of the finger 19A to the right andleft.

Referring to FIGS. 7-8, the finger 19A includes a linkage 43. One end ofthe linkage 43 is rotatably connected to phalange 38A by joint 44A suchthat the linkage 43 is selectively rotatably with respect to phalange38A about an axis that is parallel to axes A1, A2, and A3. The other endof the linkage 43 is rotatably connected to phalange 38C by joint 44Bsuch that the linkage 43 is selectively rotatable with respect tophalange 38C about an axis that is parallel to axes A1, A2, and A3.Accordingly, phalanges 38A-38C and linkage 43 cooperate to define afour-bar linkage.

Referring to FIG. 9, wherein like reference numbers refer to likecomponents from FIGS. 1-8, movement of the phalanges 38A-38D aboutjoints 42A-42D is accomplished by robotic tendons 46A-46D, i.e.,flexible members such as cables. Each of the tendons 46A-46D isoperatively connected to a respective actuator (shown at 26 in FIG. 3)in the forearm (shown at 24 in FIG. 3). In an exemplary embodiment, theactuators 26 are electric motors operatively connected to the tendons46A-46D by drive mechanisms configured to convert the rotary motion ofthe motors to linear motion to drive the tendons 46A-46D. The placementof the actuators and drive mechanisms in the forearm 24 and/or wristcontributes to the compactness of the hand 18.

The routing of the tendons 46A-46D with respect to the joints 42A-D andthe axes A1-A4 enables the finger 19A to be fully controlled throughthree degrees of freedom using only the four tendons 46A-46D. Twoopposing tendons 46A, 46B control the medial pitch joint 42B, and twoopposing tendons 46C, 46D control the proximal pitch joint 42A. One endof tendon 46B is operatively connected to phalange 38B on one side ofjoint 42B and axis A2 such that tension in tendon 46B causes rotation ofphalange 38B with respect to phalange 38A about axis A2 in a firstdirection 48. One end of tendon 46A is operatively connected to phalange38B on the opposite side of joint 42B and axis A2 from tendon 46B suchthat tension in tendon 46A causes rotation of phalange 38B with respectto phalange 38A about axis A2 in a second direction 52 opposite thefirst direction 48.

One end of tendon 46D is operatively connected to phalange 38A on oneside of joint 42A and axis A1 such that tension in tendon 46D causesrotation of phalange 38A with respect to phalange 38D about axis A1 inthe first direction 48. One end of tendon 46C is operatively connectedto phalange 38A on the opposite side of joint 42A and axis A1 fromtendon 46D such that tension in tendon 46C causes rotation of phalange38A with respect to phalange 38D about axis A1 in the second direction52. Rotation of the phalanges in the first direction 48 causes thephalanges to rotate toward the palm 36, as shown in FIGS. 5-6, and thusrotation of the phalanges in the first direction 48 enables the hand 18to grip an object. Rotation of the phalanges in the second direction 52causes the phalanges to rotate away from the palm 36, and thus causesthe finger 19A to release a grip on the object.

Referring again to FIGS. 7-8, joint 42C is kinematically linked to joint42B via linkage 43, and thus the angular position of joint 42C isdependent upon the angular position of joint 42B. Accordingly, therotational position of phalange 38C with respect to phalange 38B isdependent upon the rotational position of phalange 38B with respect tophalange 38A. More specifically, the angle β formed between phalanges38C and 38B is determined by the angle α formed between phalanges 38Band 38A: decreasing α causes a corresponding decrease in β. An exemplaryrelationship between the rotational position of joint 42C and joint 42Bis depicted in FIG. 10.

Referring to FIG. 10, the angle of joint 42C is shown as a function ofthe angle of joint 42B. It may be desirable for the function to be aslinear as the design constraints of the finger 19A will allow. The fourbar linkage comprising phalanges 38A-38C and linkage 43 is designed suchthat the linkage 43 is a straight line member between its end shafts,and is in tension during grasping. Linkage 43 in one embodiment is arigid member; in another embodiment, linkage 43 is a compliant member,such as a spring, to achieve compliance of the distal pitch joint 42Cduring grasping.

Accordingly, tendons 46A and 46B control the position of joint 42C viatheir control of joint 42B. A human finger is generally considered tohave four independently controllable degrees of freedom. Bykinematically linking joints 42B and 42C, finger 19A effectivelyapproximates the poses achievable by a human finger with only threeindependently controllable degrees of freedom, thereby eliminating thetendons that would be required to control joint 42D independently.

Referring to FIG. 11, wherein like reference numbers refer to likecomponents from FIGS. 1-11, there are no tendons dedicated tocontrolling the position of the yaw joint 42D. Instead, tendons 46A and46B are routed on one side of joint 42D and axis A4, and tendons 46C and46D are routed on another side of joint 42D and axis A4. The balance oftension in these four tendons 46A-46D is manipulated to control theposition of joint 42D and, correspondingly, the angular position ofphalanges 38A-38D with respect to the base structure 34.

Referring to FIG. 12, the finger 19A includes at least two types ofsensors. More specifically, the sensors of the finger 19A includetactile load cells 54A-54C, each of which is mounted to a respectivephalange 38A-38C. The finger 19A also includes a plurality of jointposition sensor assemblies 56A-56C, each of which is configured tomeasure the absolute angular position of a respective one of the joints42A-42C and the relative angular position of a phalange relative to aconnecting phalange. Each of the joint position sensor assemblies56A-56C includes a respective magnet 58A-58C and a respective Halleffect sensor 62A-62C.

Referring to FIG. 13, sensor assembly 56A is representative of sensorassemblies 56B and 56C, and thus magnet 58A and sensor 62A arerepresentative of magnets 58B, 58C and sensors 62B, 62C, respectively.Magnet 58A is rigidly mounted with respect to phalange 38D, and sensor62A is rigidly mounted with respect to phalange 38A. Magnet 58A ischaracterized by two portions 66, 70. Portion 66 is a segment of acircle having a center point 74 on axis A1. Portion 70 is a segment of acircle having a center point at 78. The north pole N of the magnet 58Ais disposed at one intersection of the portions 66, 70, and the southpole S of the magnet 58A is disposed at the other intersection of theportions 66, 70. In the embodiment depicted, portion 66 has the sameradius as portion 70, and the concave sides of portions 66, 70 face oneanother. The magnet 58A circumscribes both center points 74, 78.

Sensor 62A is positioned on phalange 38A such that, as phalange 38Arotates with respect to phalange 38D about axis A1, the sensor 62Amaintains a constant distance from portion 66 of the magnet 58A. Theshape of the magnet 58A and the placement of the sensor 62A provide alinear relationship between angular position of the phalange 38A withrespect to phalange 38D and the change in magnetic field that is read bysensor 62A. In the embodiment depicted, sensor assembly 56A generates anapproximately linear signal over a 150-degree usable range of angularpositions.

Magnet 58A is mounted with respect to phalange 38D and sensor 62A ismounted with respect to phalange 38A, and thus sensor assembly 56Ameasures the rotational position of phalange 38A with respect tophalange 38D. Magnet 58B is mounted with respect to phalange 38B andsensor 62B is mounted with respect to phalange 38A, and thus sensorassembly 56B measures the rotational position of phalange 38B withrespect to phalange 38A. Magnet 58C is mounted with respect to phalange38C and sensor 62C is mounted with respect to phalange 38B, and thussensor assembly 56C measures the rotational position of phalange 38Cwith respect to phalange 38B. A sensor assembly (not shown)substantially identical to sensor assemblies 56A-56C measures theposition of phalange 38D with respect to base member 37 as phalange 38Drotates about axis A4.

In the embodiment depicted, the range of motion of joint 42A (proximalpitch) is −10° to 95°; the range of motion of joint 42B (medial pitch)is 0° to 120°; the range of motion of joint 42C (distal pitch) is 0° to70°; and the range of motion of joint 42D (yaw) is −20° to 20°.

Referring to FIGS. 12 and 14, finger 19A is mounted to the basestructure 34 by a shock mount 82. The shock mount 82 includes a keyedshaft 86, a retainer ring 90, and a spring 94. The cylindrical shaft 86is slidingly engaged within a cylindrical cavity 98 defined by the basestructure 34. The rectangular key 102 extends within a rectangularportion 106 of cavity 98 to prevent rotation of the shaft 86 withrespect to the structure 34. The retainer ring 90 is larger than thecavity 98 and thus retains the shaft 86 inside the cavity 98. The spring94 biases the shaft 86 outward and absorbs shocks that may be exerted onthe finger 19A.

It should be noted that, although the tendons 46A-46D are depicted inFIGS. 9 and 11 as being external to the phalanges 38A-38D, each of thetendons is routed through a respective internal guide channel. In theembodiment depicted, tendons 46A-46D are braided polymers. Referring toFIG. 15, the finger 19A includes inserts, such as the ones shown at110A, 110B, 110C, where sliding friction of the tendons 46A-46D occurs.The inserts 110A, 110B, 110C are softer and weaker than the structuralmaterial of the phalanges 38A-38D, and are selectively replaceable. Inone embodiment, the tendons 46A-46D comprise Vectran® and the inserts110A, 110B, 110C are bronze.

Referring to FIGS. 16 and 17, the finger 19A is configured toaccommodate, for each pair of opposing tendons, a respectivebidirectional tendon terminator 114A, 114B. More specifically, tendon46A extends on the non-palmar, or dorsal, side of axes A1 and A2, and ismounted to phalange 38B via tendon terminator 114A. Tendon 46B extendson the palmar side of axes A1 and A2, and is mounted to phalange 38B viatendon terminator 114A. Similarly, tendon 46C extends on the non-palmarside of axis A1 and is mounted to phalange 38A by tendon terminator114B. Tendon 46D extends on the palmar side of axis A1 and is mounted tophalange 38A by tendon terminator 114B.

Referring to FIG. 18, a phalange 38 is shown in a cutaway, perspectiveview. Phalange 38 is representative of phalanges 38A-38C, and sensor 54is representative of sensors 54A-54C. Phalange 38 defines a chamber 118that is characterized by an opening 122. Compact electronics 126 arecontained within the chamber 118. The functions of the electronics 126include providing power to the sensors, collecting analog sensor data,converting analog signals to digital signals, multiplexing digitalsignals, and communicating data to upstream electronics. Referring againto FIG. 16, the finger 19A includes a central channel 128 that extendsthe length of the finger 19A to accommodate the wiring required toconnect the sensors, the compact electronics, and the upstreamelectronics.

Referring to FIGS. 18 and 19, sensor 54 includes a sensor cover 130 anda sensor assembly 134. The sensor assembly 134 generates sensor signalsin response to loads applied to the sensor cover 130, and transmits thesensor signals to the electronics 126. The sensor assembly 134 isgenerally C-shaped, and is characterized by a flange 138, 142 at eachend. Each flange 138, 142 abuts a respective shoulder 146, 150 formed bythe phalange 38. The flanges 138, 142 of the sensor assembly 134 alsopartially define respective slots 154, 158.

A C-shaped clip 162 includes a flange 166, 170 at each end. The clip 162extends across opening 122 to enclose the chamber 118 and theelectronics 126 contained therein. Each flange 166, 170 engages arespective one of the slots 154, 158 to secure the clip 162 to thesensor assembly 134, and to retain the sensor assembly 134 to thephalange 38. The cover 130 is mounted to the sensor assembly 134 byscrews 174.

Referring again to FIG. 16, the finger 19A is designed to accommodate aglove or skin-like covering (not shown) for protection from theenvironment and to provide grip surfaces to the tactile sensors that areappropriate for a specific task. The finger 19A includes a plurality ofthreaded attachment holes 178 designed to secure the glove or skin-likecovering to the finger, preventing slippage at the critical locations.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims

The invention claimed is:
 1. A robotic hand assembly comprising: a basestructure; a finger having first, second, and third phalanges; a firstjoint operatively connecting the first phalange to the base structuresuch that the first phalange is selectively rotatable with respect tothe base structure about a first axis; a second joint operativelyconnecting the second phalange to the first phalange such that thesecond phalange is selectively rotatable with respect to the firstphalange about a second axis; and a third joint operatively connectingthe third phalange to the second phalange such that the third phalangeis selectively rotatable with respect to the second phalange about athird axis; a first tendon being operatively connected to the secondphalange such that tension in the first tendon urges the second phalangeto rotate about the second axis in a first direction; a second tendonbeing operatively connected to the second phalange such that tension inthe second tendon urges the second phalange to rotate about the secondaxis in a second direction; a third tendon being operatively connectedto the first phalange such that tension in the third tendon urges thefirst phalange to rotate about the first axis in the first direction; afourth tendon being operatively connected to the first phalange suchthat tension in the fourth tendon urges the first phalange to rotateabout the first axis in the second direction; wherein the third joint iskinematically linked to the second joint such that the position of thethird phalange with respect to the second phalange is determined by theposition of the second phalange with respect to the first phalange. 2.The robotic hand assembly of claim 1, further comprising a linkage thatis rotatably mounted with respect to the first phalange and rotatablymounted with respect to the third phalange to kinematically link thethird joint and the second joint.
 3. The robotic hand assembly of claim2, wherein the linkage includes a spring.
 4. The robotic hand assemblyof claim 1, further comprising a fourth phalange rotatably connected tothe first phalange by the first joint; and a fourth joint operativelyconnecting the fourth phalange to the base structure such that thefourth phalange is selectively rotatable with respect to the basestructure about a fourth axis.
 5. The robotic hand assembly of claim 4,wherein the fourth axis is substantially perpendicular to the first,second, and third axes.
 6. The robotic hand assembly of claim 5, whereinthe first and second tendons are routed on a first side of the fourthaxis; and wherein the third and fourth tendons are routed on a secondside of the fourth axis.
 7. The robotic hand assembly of claim 1,further comprising at least one insert; wherein at least one of thefirst, second, third, and fourth tendons contacts the insert; andwherein the insert is softer or weaker than the phalanges.
 8. Therobotic hand assembly of claim 1, further comprising a shock mount thatoperatively connects the finger to the base structure.